The present invention relates to a member required to have bonding strength, airtightness and other properties as in the case of bonding a metal to a ceramic. More particularly, the invention relates to a process for producing a ceramic member for bonding, a ceramic member for bonding, a bonded object, a vacuum switch, and a vacuum vessel.
The molybdenum-manganese method (Moxe2x80x94Mn method; Telefunken method) has conventionally been known as a method for metallizing a surface of a ceramic base.
This Moxe2x80x94Mn method comprises applying a metallizing ink prepared by adding a bonding aid such as Mn powder, Ti powder and glass ingredient (SiO2) to a powder of high-melting metal such as tungsten and molybdenum and mixing the powder mixture with an organic binder to make a paste to a ceramic base, and then baking the ink layer (baking method).
The technique of the related art described above necessitates a baking temperature as high as from 1,300 to 1,500xc2x0 C. for metallization and, hence, has had a problem that the sintering cost regarding furnace structure, utilities, expendable heat-resistant materials, etc. is high.
Another problem is that the ceramic itself deforms in the high-temperature baking, resulting in a product which does not satisfy dimensional accuracy.
Although a measure in overcoming the problem described above may be to bake a metallizing ink having a conventional composition at a temperature lower than 1,300xc2x0 C., this low-temperature baking poses a problem that a sufficient bonding strength cannot be obtained.
Furthermore, in the case where a metallic layer formed by metallization by the Moxe2x80x94Mn method is to be bonded to another metallic member or the like by brazing, it is necessary to improve the wettability thereof by a brazing material so as to obtain satisfactory bonding. Although it is hence inevitable to conduct post-treatments such as nickel plating and subsequent sintering, there has been a problem that these post-treatments make the production process complicated.
Further, in recent years, a technique has been proposed which comprises applying a tungsten paste to a ceramic base to form a lower layer (sublayer), applying a nickel paste to the lower layer, baking the coated material, and then subjecting the material directly to brazing for the purpose of reducing the number of steps (see xe2x80x9cElectronic Ceramicsxe2x80x9d, December 1991). However, this technique leaves something to be desired because it requires a baking temperature as high as not lower than 1,250xc2x0 C., adding to the sintering cost and deteriorating the dimensional accuracy of the resulting ceramic product.
The invention has been worked out in order to solve the aforementioned problems. An aim of the invention is to provide a process for producing a ceramic member for bonding which enables low-temperature sintering and simplified production process and gives a high dimensional accuracy, and a ceramic member for bonding, a bonded object, a vacuum switch and a vacuum vessel produced thereby.
(1) In order to accomplish the aforementioned aim of the invention, the first essence of the invention lies in a process for producing a ceramic member for bonding, which comprises:
A first step of applying a lower layer paste prepared from a first mixture comprising nickel, tungsten and molybdenum to the surface of a ceramic base which is a sintered ceramic, and then drying the coating layer to form a lower layer;
A second step of applying an upper layer paste prepared from a second mixture of nickel or nickel oxide and at least one of copper, copper oxide, manganese and manganese oxide to the lower layer, and then drying the coating layer to form an upper layer; and
A third step of heating and baking the lower layer and the upper layer.
In the invention, a mechanism of bonding of a Moxe2x80x94Wxe2x80x94Ni layer which is a lower layer to a ceramic base is formed. For the aforementioned baking (i.e., sintering the lower layer and the upper layer by calcining), the addition of Nickel causes the acceleration of sintering of Molybdenum particles, enabling low temperature sintering. Further, since the lower layer paste comprises tungsten incorporated therein, the sintering rate of Molybdenum particles can be relaxed to accomplish fair bonding over a wide temperature range.
Moreover, in the invention, a mechanism of bonding of a Nixe2x80x94(Cu, Mn) layer which is an upper layer to a Moxe2x80x94Wxe2x80x94Ni layer which is a lower layer is formed. For the aforementioned baking, the incorporation of copper or manganese in the upper layer causes the drop of melting point of nickel, making it possible to form a dense alloy layer on the lower layer. In this arrangement, fair brazing can be effected even without nickel plating and subsequent sintering. Further, since the upper layer is an alloyed layer, the excessive diffusion of nickel in the lower layer containing molybdenum can be lessened, making it possible to prevent strength drop due to oversintering of molybdenum.
In the invention, the aforementioned action allows omission of nickel plating and sintering therefor, which has heretofore been required, making it possible to drastically simplify the production process and hence drastically reduce the production cost. Further, the lower layer and the upper layer can be sintered at a temperature as low as not higher than 1,200xc2x0 C., the sintering cost regarding furnace structure, utilities, expendable heat-resistant materials, etc. can be reduced. Moreover, the low temperature sintering makes it difficult for the ceramic itself to deform and hence makes it possible to obtain a high dimensional accuracy.
The lower layer paste can be prepared by mixing a first mixture containing a nickel powder, a tungsten powder and a molybdenum powder with an organic binder. The upper layer paste can be prepared by mixing a second mixture containing a nickel powder or nickel oxide powder with at least one of a copper powder, copper oxide powder, manganese powder and manganese oxide powder or a second mixture containing a nickel-copper alloy powder or nickel-manganese alloy powder with an organic binder.
When baking at the third step is effected in a humidifying reducing atmosphere such as H2 and H2/N2, particularly at a temperature of from 1,080xc2x0 C. to 1,200xc2x0 C., the resulting product has a high bonding strength and airtightness to advantage.
(2) The second essence of the invention lies in the aforementioned process for producing a ceramic member for bonding, wherein the first mixture comprises nickel, tungsten and molybdenum incorporated therein in an amount of from 1% to 10% by weight, from 20% to 69% by weight and from 30% to 69% by weight, respectively.
In the invention, since the content of nickel in the first mixture is not lower than 1% by weight, nickel reacts with molybdenum, which is a high melting metal, to accelerate sintering of the lower layer (metallic layer). In this manner, sintering can be thoroughly effected even at low temperatures. Further, since the content of nickel in the first mixture is not greater than 10% by weight, oversintering of molybdenum can be prevented, making it possible to prevent the lack of strength of bonding between the ceramic base and the metallic layer.
Moreover, since the content of tungsten in the first mixture is not lower than 20% by weight, the temperature range within which a high strength metallic layer can be formed is wide. Further, since the content of tungsten in the first mixture is not greater than 69% by weight, the incorporation of molybdenum and nickel exerts an effect of preventing undersintering at low temperatures.
Further, since the content of molybdenum in the first mixture is not lower than 30% by weight, a firm metallic layer can be formed at low temperatures. Moreover, since the content of molybdenum in the first mixture is not greater than 69% by weight, the incorporation of tungsten and nickel can exert a good effect.
Examples of materials other than the metallic ingredients of the lower layer paste include organic binder.
(3) The third essence of the invention lies in the process for producing a ceramic member for bonding according to the first or second essence of the invention, wherein the first mixture further comprises a silicon oxide component incorporated therein in an amount of from 2% to 15% by weight.
In the invention, since the first mixture comprises a silicon oxide (SiO2) ingredient incorporated therein in an amount of from 2% to 15% by weight, the resulting airtightness can be improved.
(4) The fourth essence of the invention lies in the process for producing a ceramic member for bonding according to any one of the first to third essences of the invention, wherein the second mixture comprises nickel or nickel oxide and at least one of copper, copper oxide, manganese and manganese oxide incorporated therein in an amount of from 35% to 75% by weight and from 25% to 65% by weight, respectively.
In the invention, since the content of nickel or nickel oxide in the second mixture is from 35% to 75% by weight, the resulting ceramic member for bonding exhibits an enhanced bonding strength and an excellent airtightness.
Further, since the content of at least one of copper, copper oxide, manganese and manganese oxide in the second mixture is not lower than 25% by weight, the resulting ceramic member for bonding exhibits an enhanced brazability and bonding strength. Moreover, since the content of at least one of copper, copper oxide, manganese and manganese oxide in the second mixture is not greater than 65% by weight, the lack of strength between the ceramic base and the metallic layer due to penetration of these ingredients into the metallic layer can be prevented.
Examples of materials other than the metal and metal oxide ingredients of the upper layer include organic binder.
When the content of the silicon oxide ingredient in the second mixture is from 2% to 10% by weight, the resulting ceramic member for bonding exhibits an even higher airtightness.
(5) The fifth essence of the invention lies in a ceramic member for bonding, comprising:
A metallic layer which is a lower layer comprising nickel, tungsten and molybdenum provided on the surface of a ceramic base which is a sintered ceramic; and
An alloy layer which is an upper layer comprising nickel and at least one of copper and manganese provided on the surface of the metallic layer with or without an interlayer interposed therebetween.
In the invention, since the incorporation of nickel allows the acceleration of sintering of molybdenum particles in the lower layer, the lower layer can be sintered at low temperatures. Further, the incorporation of tungsten allows the relaxation of the sintering rate of molybdenum particles, making it possible to provide an excellent bonding over a wide temperature range.
Moreover, the incorporation of copper and manganese in addition to nickel in the upper layer causes the drop of melting point of nickel, making it possible to form a dense alloy layer on the upper layer. In this arrangement, fair brazing can be effected without nickel plating or the like. Further, since the upper layer is an alloy layer, excessive diffusion of nickel in the lower layer, which comprises molybdenum incorporated therein, can be lessened, making it possible to prevent the drop of strength due to oversintering of molybdenum.
In the invention, the aforementioned action allows the omission of nickel plating and subsequent sintering, which have heretofore been required, making it possible to drastically simplify the working procedure and hence drastically reduce the production cost. Further, the composition of the invention can be sintered at low temperatures, making it possible to reduce the sintering cost regarding furnace structure, utilities, expendable heat-resistant materials, etc. Moreover, the low temperature sintering makes it difficult for the ceramic to deform, thereby giving a high dimensional accuracy. In addition, sintering can be thoroughly effected at low temperatures, a high bonding strength can be secured.
While the alloy layer which is an upper layer maybe formed directly on the metallic layer which is a lower layer, an interlayer having a different constitution from that of these layers may be formed interposed therebetween.
(6) The sixth essence of the invention lies in the ceramic member for bonding according to the fifth essence of the invention, wherein the metallic layer comprises nickel, tungsten and molybdenum in an amount of from 0.7% to 8% by weight, from 15% to 75% by weight and from 20% to 80% by weight, respectively.
In the invention, since the content of nickel in the metallic layer is not smaller than 0.7% by weight, sintering can be thoroughly effected at low temperatures. Further, since the content of nickel in the first mixture is not greater than 10% by weight, oversintering of molybdenum can be prevented, making it possible to prevent the lack of strength of bonding between the ceramic base and the metallic layer.
Further, since the content of tungsten is not lower than 15% by weight, the temperature range within which a firm metallic layer can be formed is wide. Moreover, since the content of tungsten is not greater than 75% by weight, the incorporation of molybdenum and nickel can exert a good effect.
Further, the metallic layer comprises molybdenum incorporated therein in an amount of from 20% to 80% by weight and thus forms a firm metallic layer.
(7) The seventh essence of the invention lies in the ceramic member for bonding according to the fifth or sixth essence of the invention, wherein the metallic layer further comprises a silicon oxide component incorporated therein in an amount of from 3% to 18% by weight as calculated in terms of oxide.
In the invention, since the metallic layer comprises a silicon oxide component incorporated therein in an amount of from 3% to 18% by weight, the adhesion between the ceramic member and the metallic layer is extremely high, enhancing airtightness.
(8) The eighth essence of the invention lies in the ceramic member for bonding according to any one of the fifth to seventh essences of the invention, wherein the alloy layer comprises nickel, copper and manganese incorporated therein in an amount of from 10% to 75% by weight, from 20% to 85% by weight and from 5% to 40% by weight, respectively.
In the invention, the alloy layer comprises nickel in an amount of from 10% to 75% by weight and thus exhibits a bonding strength with the metallic layer and a high airtightness.
Further, since the content of copper is not smaller than 20% by weight, the resulting alloy layer exhibits an excellent brazability and a high strength. Moreover, since the content of copper is not smaller than 85% by weight, it contributes to the enhancement of the strength of bonding of the ceramic base to the metallic layer.
When the aforementioned alloy layer further comprises a silicon oxide component incorporated therein in an amount of from 0.05 to 1.0 parts by weight as calculated in terms of oxide, the adhesion between the ceramic member and the metallic layer is extremely high to enhance the airtightness.
(9) The ninth essence of the invention lies in the ceramic member for bonding according to any one of the fifth to eighth essences of the invention, wherein the interlayer provided interposed between the metallic layer which is a lower layer and the alloy layer which is an upper layer is an interlayer formed by a nickel-molybdenum alloy.
The invention constitutes exemplification of the ingredients of the interlayer. This interlayer may be formed under some sintering conditions. In the case where the interlayer exists, there occurs little change in properties such as bonding strength.
(10) The tenth essence of the invention lies in a bonded object comprising a metallic member bonded to a ceramic member for bonding according to any one of the fifth to ninth essences of the invention with at least the metallic layer and the alloy layer provided interposed therebetween.
In the invention, a ceramic member for bonding and a metallic member are bonded to each other with the aforementioned metallic layer and alloy layer provided interposed therebetween. In some detail, a metallic member is bonded with, e.g., a brazing material to the alloy layer of a ceramic member for bonding prepared by forming a metallic layer on the surface of a ceramic base, and then forming an alloy layer thereon. The aforementioned interlayer may be provided interposed between the metallic layer and the alloy layer.
Accordingly, nickel plating (on the surface of the metallic layer) and subsequent sintering as conventionally effected are not necessary, making it possible to braze the metallic member directly to the alloy layer. This reduces the number of production steps and hence the production cost. Further, this bonded object has a high bonding strength and a high dimensional accuracy.
(11) The eleventh essence of the invention lies in a bonded object comprising another ceramic member for bonding bonded to a ceramic member for bonding according to any one of the fifth to ninth essences of the invention with at least the metallic layer and the alloy layer provided interposed therebetween.
In the invention, a ceramic member for bonding and another ceramic member for bonding are bonded to each other with the aforementioned metallic layer and alloy layer provided interposed therebetween. The aforementioned interlayer may be provided interposed between the metallic layer and the alloy layer.
An example of such an arrangement is a bonded object having two ceramic members for bonding comprising a metallic layer and an alloy layer formed thereon bonded to each other at the alloy layer thereof with a brazing material.
Accordingly, as in the tenth essence of the invention, nickel plating and subsequent sintering as conventionally effected are not necessary, making it possible to braze the metallic member directly to the alloy layer. This reduces the number of production steps and hence the production cost. Further, this bonded object has a high bonding strength and a high dimensional accuracy.
(12) The twelfth essence of the invention lies in a vacuum switch comprising a bonded object according to the tenth or eleventh essence of the invention.
The invention concerns a vacuum switch comprising the aforementioned bonded object. An example of this vacuum switch is an electric circuit switch comprising a ceramic insulating valve suitable particularly for switching of high-voltage large-current electricity.
(13) The thirteenth essence of the invention lies in a vacuum vessel comprising a bonded object according to the tenth or eleventh essence of the invention.
The invention concerns a vacuum vessel (e.g., insulating valve) used in the aforementioned vacuum switch, etc. A vacuum switch (electrical circuit switch) can be fabricated by disposing electrodes and other necessary members in this vacuum vessel.
In the case where there is contained the aforementioned silicon oxide component, the proportion of other ingredients of the various essences of the invention (metals and oxide thereof) may be properly adjusted within their predetermined range such that the sum of the content of all these ingredients is 100% by weight depending on the content of the silicon oxide component.